class Solution {
    public int romanToInt(String s) {
        int sum = 0;
        int num = f1(s.charAt(0));
        for(int i = 1;i < s.length();i++) {
            int numss = f1(s.charAt(i));
            if(num < numss) {
                sum -= num;
            } else {
                sum += num;
            }
            num = numss;
        }
        sum += num;
        return sum;
    }

    private int f1(char hh) {
        switch(hh) {
            case 'I':return 1;
            case 'V':return 5;
            case 'X':return 10;
            case 'L':return 50;
            case 'C':return 100;
            case 'D':return 500;
            case 'M':return 1000;
            default: return 0;
        }
    }
}